Compositions for Deicing/Anti-Icing

ABSTRACT

A non-toxic deicing/anti-icing fluid includes at least 20% by weight of a freeze point depressant selected from short chain polyols having 3 to 5 carbon atoms. The fluid further includes at least 10% by weight of water, a thickener, a surfactant, and a pH moderator. The fluid meets the requirements of SAE/AMS 1428 or its revisions for a non-Newtonian, Type II, III, or IV aircraft deicing/anti-icing fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/305,312, filed Feb. 17, 2010, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

This invention relates in general to improved, thickened, fluidcompositions to remove ice, frost, and snow from surfaces and/or toprevent ice from forming on surfaces. More specifically, in certainembodiments, this invention relates to formulation ofenvironmentally-friendly, non-Newtonian fluids, primarily for aircraftdeicing/anti-icing, as required per Society of Automotive EngineersAerospace Material Specification (SAE/AMS) 1428. However, otherapplications of deicing/anti-icing, such as wind-turbine blades andthird-rail where the rail is for making electrical contact, are alsopossible.

Several types of aircraft deicing/anti-icing fluids (ADFs/AAFs) are usedto remove deposits of ice, frost and snow from aerodynamically-criticalsurfaces before an aircraft can safely lift off the runway.Additionally, the film of such a liquid, left on the aircraft, providessome protection from refreezing of water due to freezing precipitation.The anti-icing property of these fluids can be quantified by the WaterSpray Endurance Test (WSET), which is fully described in SAE/AMS 1428Specification. Four different types of ADF/AAFs, namely Types I, II,III, or IV, can be qualified for use on an aircraft, depending on howthe fluid is used and the anti-icing protection achieved. The anti-icingprotection requirement for Type I fluids is only 3 minutes, with TypesII and IV being 30 and 80 minutes, respectively. To achieve the muchlonger WSET times for Types II and IV fluids, the fluids are thickenedand these exhibit non-Newtonian (pseudoplastic) behaviors, also referredto as shear-thinning behavior. The shear thinning behavior allows formaximum anti-icing protection due to the uniform coverage by a highviscosity fluid when the aircraft is stationary (zero shear). This fluidgreatly thins out during an aircraft take-off roll as the shear raterapidly increases, which allows the aircraft to shed the majority of thefluid, thus restoring the aerodynamics of the airfoil.

The primary difference between Type II and Type IV fluids is that a TypeII can be used both for deicing and anti-icing while Type IV is usedjust for anti-icing after a deicing step is completed. In either case,such fluids typically contain a mixture of a glycol, such as ethyleneglycol (EG) or diethylene glycol (DEG) or propylene glycol (PG) withwater, the glycol plus water typically adding up to more than 95% byweight (wt %). These fluids also contain additives such as thickeners,surfactants, anti-foamers, corrosion inhibitors, anti-precipitants, anddyes to meet the specifications. All of these chemicals are of potentialconcern to airports as they are required to obtain storm water dischargepermits under the applicable environmental protection agencies. Theconcerns are: (a) high levels of oxygen demand due to naturalbiodegradation of glycols; (b) mammalian toxicity of some glycols, suchas EG (which is also a hazardous air pollutant) and DEG; (c) toxicity ofdegradation products of commonly-used surfactants; (d) toxicity andnon-biodegradability of commonly used corrosion inhibitors and otheradditives.

The vast majority of Type II and IV fluids use PG as a freeze-pointdepressant but it has a high chemical oxygen demand (COD) and biologicaloxygen demand (BOD). The thickened fluids typically use alkylphenolethoxylate (APE) surfactants, the biodegradation products of which havebeen shown to be endocrine disruptors, and as such these are banned inEurope and are under EPA scrutiny in the U.S. A number of fluids alsouse benzyltriazole or tolytriazole corrosion inhibitors, which are toxicand non-biodegradable and thus persist in the environment.

The thickened fluids of prior art typically use large molecules(polymers) that typically thicken by molecular entanglement or gelationdue to pH adjustment. These polymers often have performance deficienciesas they leave gel-forming residues on aircraft surfaces. The quantity ofresidue is typically proportional to the amount of thickener (polymer)used as that is the primary controller of viscosity and rheology.Additionally, these thickeners typically have relatively flat viscosityvs. temperature curve in the 20° C. to −30° C. range. If a certain, highviscosity is targeted for the 0 to −10° C., which is the majority ofoperating range, one gets undesirably high viscosities at 20° C. whichmakes fluid preparation and handling harder as well as at temperaturebelow −10° C. which makes aerodynamic performance poorer and the gelresidue problem worse.

Various patents are known that describe some of the approaches, partialsolutions, and inherent problems for addressing the requirements foraircraft anti-icing. However, the thickened aircraft fluids described inthe patents have functional and/or environmental deficiencies. Thefunctionally superior formulations rely on use of components that wererecently recognized as environmentally unfriendly and are in variousphases of being banned. A high performance, environmentally friendly,thickened aircraft fluid is therefore desired. Such fluids may also beuseful for other applications, such as (a) deicing/anti-icing ofwind-turbine blades and (b) stationary surfaces such as the third railfor electric trains.

SUMMARY OF THE INVENTION

This invention relates to improved compositions for deicing/anti-icing.In certain embodiments, the composition is an environmentally-friendlydeicing/anti-icing fluid, which includes short chain polyols having 3 to5 carbon atoms, and mixtures thereof, a thickener, nonionicsurfactant(s), and other additives, which is functionally superior toprior-art fluids with respect to its anti-icing properties. This fluidin certain embodiments is non-toxic to mammalians and can typically haveat least a 25 lower aquatic toxicity.

Also, in certain embodiments, the deicing/anti-icing fluids meet orexceed the requirements of SAE/AMS 1428, especially Type IV anti-icingfluids with a freeze point below −32° C. and a WSET of over 80 minutesin an undiluted form. The fluids may also be used as a Type II fluid fordeicing and anti-icing with a WSET above 30 minutes for undiluted fluid.

In certain embodiments, the compositions include bio-based C₃-C₅polyols, such as PG, glycerol, and xylitol, to substantially reduce thecarbon footprint of the fluid.

In certain particular embodiments, the compositions eliminate the use oftoxic surfactants such as alkylphenol ethoxylates (APEs) and/or toxiccorrosion inhibitors such as triazoles (e.g., benzyltriazoles) used inprior-art fluids, thus lowering the aquatic toxicity with LC₅₀ (lethalconcentration above which 50% of species such as fathead minnows ordaphnia magna die, at conditions described in AMS 1428) values of atleast 1,000 mg/L (the higher the value, the lower the toxicity).

In other embodiments, the compositions include associative polymers,such as cross-linked polyacrylic acid copolymers, in combination withnon-NPE surfactants that strongly associate (interact) with the polymersto achieve desired thickening at freezing temperatures withsubstantially reduced polymer usage, and thus improved preparation andhandling of the fluid due to a lower viscosity at warmer temperatures.

In certain embodiments, the compositions include mixtures of glyceroland other petroleum-based or bio-based C₃-C₅ polyols to reduce theCOD/BOD of the fluid as well as to achieve desired thickening with areduced quantity of thickener, which minimizes the formation ofgel-forming residues on aircraft surfaces.

In other embodiments, the compositions include environmentally friendlyanti-precipitants or chelating agents to give protection from hardnessions, such as calcium, if the fluid is to be diluted, while reducing therequirement for corrosion inhibitors and thus reduce the toxicity of thefluid.

Also, in certain embodiments, the compositions include non-foaming orlow-foaming, nonionic surfactants that associate with the polymericthickener to reduce or eliminate the use of anti-foamers, furtherreducing the toxicity of the fluid.

Various additional aspects of the compositions will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiments and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot showing viscosity at different temperatures ofanti-icing fluids.

FIG. 2 is a plot showing the effect of associating anti-precipitantconcentration on viscosity at different temperatures ofdeicing/anti-icing fluids.

FIG. 3 is a plot showing the effect of a pH modifier on viscosity atdifferent temperatures of deicing/anti-icing fluids.

FIG. 4 is a plot showing the effect of associating surfactant andglycerol on viscosity at different temperatures of deicing/anti-icingfluids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As previously mentioned, a fluid with strong anti-icing propertiesmeeting the specifications in SAE/AMS 1428 contains, as a minimum, afreeze point depressant (FPD), water, a thickener, and a surfactant.Other additives to manage dilution by hard water, foaming on spraying,inhibit corrosion, and to give the required color to the formulation,may be added. All ingredients except water can potentially degrade theenvironment on discharges after application. We have discoveredcompositions that, in certain embodiments, eliminate the toxiccomponents while maintaining or exceeding the functional requirements ofaircraft deicing/anti-icing.

The viscosity, rheology, and surface activity of an anti-icingformulation are significant for achieving anti-icing properties. Atypical prior-art, anti-icing fluid uses a shear thinning thickener, soas to easily shed off an aircraft on takeoff due to application ofshear, which produces a relatively flat viscosity curve on chilling, asshown in FIG. 1. The curves (A) and (B) are based on use of naturalthickener, xanthan gum (Ref.: U.S. Pat. No. 5,772,912). As shown, up toabout 0.5% thickener is needed to reach a viscosity of 60,000 cP at −5°C., but this makes the 20° C. viscosity about 55,000 cP, which is thickfor fluid preparation and handling. Also, a viscosity of 65,000 cP at−20° C. is unlikely to pass aerodynamic acceptance test. Curves (C) and(D) are examples of formulations we have made that show rapid viscosityrise on chilling from 20° C. down to freezing temperature, using onlyabout 0.2% or less thickener and especially, non-NPE associatingsurfactants. Among these two latter curves, the formulation (D) is moreattractive as it shows a decline in viscosity after about −5° C. to −10°C., which allows the fluid to have excellent anti-icing behavior whilenot being too thick to pass aerodynamic acceptance test (SAE/AMS 1428)at temperatures below −20° C. Rapidly rising and then falling viscosityon chilling is desired over flat curves in some applications. Asdescribed in more detail below, these special effects on viscosity arein some embodiments based on using special surfactants and potentially aspecial FPD blend. In some embodiments, these viscosity properties areprovided by the interaction between surfactant(s) and polymericthickener(s).

In certain embodiments, the present compositions are useful as anenvironmentally friendly and functionally superior deicer/anti-icer,primarily for use on aircrafts, that contains a mixture of C₃-C₅ polyolsand water, the total weight of which is about 95-99%. Some examples ofFPDs are glycerol; 1,2 propanediol (a C₃ polyol, commonly referred to aspropylene glycol (PG)); 1,3 propanediol (C₃, PDO); DEG (C₄); and xylitol(C₅), among others. The COD of PG, which is the most widely used FPD inType II and IV fluids, is 1.68 kg O₂/kg fluid. The COD values ofglycerol and xylitol, on the other hand, are 1.22 and 1.16 kg O₂/kgrespectively. Therefore, glycerol and xylitol are preferred forlower-COD fluids. In certain embodiments, to optimize certain physicalproperties, these are used in combination with other C₃-C₅ polyols. Therelative proportions of the FPD and water can be varied to obtain afreeze point below −32° C. The FPDs can be biobased (e.g., derived fromplants) or non-biobased (e.g., derived from petroleum or othermaterials).

In certain embodiments, the fluid composition includes a thickener whichassociates with surfactant(s) and some FPDs to achieve optimum viscosityand rheology, allowing viscosity at temperature of formulation to below, viscosity at typical operating temperatures to be high enough toobtain a high WSET value, and providing a medium viscosity at very lowtemperatures. This thickener-surfactant association may provide asynergistic effect on thickening, thereby reducing the amount ofthickener needed. The associative polymers are water-soluble. Examplesof thickeners are synthetic polymers of carboxylic acid group, such aspolyacrylic acid (PAA). The polymers may be lightly cross-linked(co-polymerized) with hydrophobic monomers/macromonomers to allowassociation with hydrophobic portions of surfactants. The typicalconcentration of the polymers thickener is 50 ppm to 0.5 wt %,preferably 0.1 to 0.2 wt %. These polymers are typically partiallyneutralized with an alkali such as potassium or sodium hydroxides or analkylamine, to achieve a pH value of 6.5 to 8.5, with a preferred valuebeing 6.9 to 7.5. A particular alkali is potassium hydroxide. Otherthickeners could also be useful.

In certain embodiments, the surfactant has a synergistic effect onthickening, thereby reducing the amount of thickener needed.

In certain embodiments, the compositions are useful as aircraftanti-icing fluids (AAF's). These fluids can be more difficult toformulate than aircraft deicing fluids (ADF's).

The rheology of an AAF or ADF can depend on several ingredients that areused for functions other than thickening: surfactant for improvedwetting, alkali for pH modification, the freezing point depressant(s),and chelating agent for anti-precipitation.

In certain embodiments, fluid composition includes one or more non-ionicsurfactants to not only provide for a reduction in the surface tensionof the FPD to obtain uniform coverage of the aircraft surfaces, but toalso enhance the thickening effect of the polymeric thickener. While awide variety of nonionic surfactants are available, many are unsuitabledue to toxicity, lack of biodegradability, and functional performancereasons. As mentioned earlier, unlike a majority of the prior-artformulations, APEs, which are functionally excellent, are to be excludedin certain embodiments. In other embodiments, surfactants that fall outof the formulation at any temperature on dilution are excluded.Typically useful surfactants are alkoxylated branched alcohol andalkoxylated linear or secondary alcohols, with branched alcohols beingpreferred. These surfactants can have an association with the thickeneras described above. These surfactants typically have a formula,CH₃C_(n)H_(2n) O(C₂H₄O)_(y)H, which can be simplified asC_(n+1)C_(2n+3)O(EO)_(y)H. The surfactants of use typically have “n”values ranging from about 6 to 18 and “y” values ranging from about 2 to20. The hydrophilic lipophilic balance (HLB) values of these surfactantstypically vary from about 6 to 18. The surfactant(s) are to be selectedto balance their hydrophobic character, as represented by thehydrocarbon (CH₃C_(n)H_(2n)) chain and the hydrophilic character, asrepresented by the ethylene oxide (C₂H₄O) or EO units. The preferredvalues of “n”,“y”, and HLB are 8-12, 3-14, and 6-12, respectively. Insome compositions, non-foaming or low-foaming surfactants are used, forexample, surfactants having an HLB less than 10. Other types ofsurfactants could also be useful.

In certain embodiments, the fluid composition includes ananti-precipitant to manage dilution with water containing hardness ions.A variety of chelating agents, such as EDTA (sodiumethylenediaminetetraacetate) or HEDTA (sodiumhydroxyethylethylenediaminetriacetate) are used in prior art. However,EDTA or HEDTA cause excessive corrosion of certain aircraft components,which leads to the requirement of corrosion inhibitors, and which aretypically toxic; these are also inadequately biodegradable. Therefore,in certain embodiments, non-EDTA, non-HEDTA chelating agents, such aspolymeric dispersants or aminopoly-carboxylates are used. The preferredanti-precipitant helps control the viscosity of the fluid as well, asshown in FIG. 2.

The compositions may also include a pH moderator, which can be anymaterial(s) suitable for modifying or maintaining the pH of thecomposition within a certain range. Some nonlimiting examples includebasic materials such as alkali metal hydroxides (e.g., potassiumhydroxide or KOH) or triethanolamine (TEA). The pH modification can havea significant effect on the rheology of the fluid as shown in FIG. 3.

The fluid may include a defoamer if one or more of the surfactants havea high HLB value. Also, a food grade dye may be added to meetspecifications.

An unexpected observation was the beneficial thickening effect ofglycerol when combined with a thickener and surfactant. For example, onsubstituting PG with some glycerol, not only did the COD of the fluiddecline, but also the amount of polymer and surfactant needed to achievethe viscosity behavior decreased. This is illustrated in FIG. 4. Thebaseline (lowest viscosity) curve is for the case where no surfactant isadded along with the thickening polymer and the freeze point depressantis PG. When an associating surfactant is added, the viscosity increasessignificantly. Further, when a surfactant is added and some PG issubstituted by glycerol, the viscosity increases substantially. Incertain embodiments, this synergy of effect allows one to make the fluidmore environmentally friendly and also to reduce the formation ofgel-foaming residues on aircraft surfaces. A similar synergistic effectmay also be found with mixtures of glycerol and other petroleum orbio-based C₃-C₅ polyols (e.g., PG, PDO and/or xylitol).

In certain embodiments, the compositions include a non-triazole compoundto serve as a corrosion inhibitor, if needed to meet the materialscompatibility specifications for aluminum, steel, and cadmium. Thisexcludes triazole compounds such as benzotriazole and tolytriazole.Examples of less toxic corrosion inhibitors are: carboxylates,silicates, phosphonates, sulfonates, amines, and amides.

Also, in certain embodiments, a deicing/anti-icing formulation isprovided based on C₃-C₅ polyols which is partly or entirely bio-based,thus reducing the carbon footprint of the fluid. Examples of bio-basedpolyols of this invention are glycerol, PG, PDO, and xylitol, all ofwhich have been successfully utilized in our formulations.

The use of multi-function components in the compositions can minimizethe number of additives used in the compositions, thereby improving theenvironmental friendliness of the compositions by reducing corrosivityand toxicity. For example, in certain embodiments, the compositionscontain the following components: freezing point depressant(s),thickener(s), surfactant(s), pH moderator(s) and water.

The following Tables 1 and 2 show some examples of deicing/anti-icingfluids of this invention.

TABLE 1 Examples of Compositions of Deicing/Anti-Icing Fluids Wt %Preferred for Component Composition Wt % Range Type IV Fluid C3-C5Polyol  20-90 45-65 Non-NPE Nonionic Surfactant #1 0.003-0.40 0.05-0.20Non-NPE Nonionic Surfactant #2 0.002-0.20 0.01-0.10 Water  10-80 35-45Polycarboxylic Acid Thickener 0.005-0.50 0.05-0.20 Potassium HydroxideTo achieve To achieve pH of 6.5 to 8.5 pH of 6.9 to 7.5 Chelating Agent0.005-0.50 0.03-0.20 Antifoamer    0-0.20 0.05-0.10 Non-triazoleCorrosion Inhibitor    0-0.50 0.01-0.20

TABLE 2 Further Examples of Compositions of Deicing/Anti-Icing FluidsPropylene Glycol 20 85 50 50 30 0 0 0 0 Glycerol 0 0 0 0 30 0 30 40 0PDO 0 0 0 0 0 50 30 0 30 Xylitol 0 0 0 0 0 0 0 20 30 Non-NPE 0.025 0.100.20 0.14 0.20 0.40 0.15 0.25 0.30 Nonionic Surfactant #1 Non-NPE 0.0050.05 0.10 0 0.03 0.002 0.01 0.05 0.06 Nonionic Surfactant #2 Water(Balance) ~79.5 ~14.5 ~49.0 ~49.5 ~39.0 ~51.0 ~39.5 ~39.0 ~39.0Polycarboxylic 0.03 0.15 0.30 0.14 0.23 0.40 0.15 0.30 0.35 AcidThickener Potassium (6.8) (7.0) (8.5) (7.2) (7.5) (7.2) (7.5) (7.3)(7.2) Hydroxide (pH) Chelating Agent 0.025 0.05 0.10 0.08 0.20 0.10 0.050.05 0.10 Antifoamer 0.20 0 0.10 0 0.05 0.05 0.10 0 0 Non-triazole 0 00.20 0.08 0.10 0.10 0.05 0.20 0.10 Corrosion Inhibitor

1. A non-toxic deicing/anti-icing fluid comprising: at least about 20%by weight of a freeze point depressant selected from the groupconsisting of short chain polyols having 3 to 5 carbon atoms, andmixtures thereof; at least about 10% by weight of water; a thickener; asurfactant; and a pH moderator; the fluid meeting the requirements ofSAE/AMS 1428 or its revisions for a non-Newtonian, Type II, III, or IVaircraft deicing/anti-icing fluid.
 2. A fluid according to claim 1,wherein the freeze point depressant is selected from the groupconsisting of glycerol, 1,2 propanediol, 1,3 propanediol, erythritol,diethylene glycol, xylitol, and mixtures thereof.
 3. A fluid accordingto claim 2, wherein the freeze point depressant is a mixture of at least10% glycerol and another of the short chain polyols.
 4. A fluidaccording to claim 2, wherein all or a portion of the freeze pointdepressant is bio-based.
 5. A fluid according to claim 1, wherein theamount of freeze point depressant is about 45-65% by weight to meet therequirements of a Type IV fluid.
 6. A fluid according to claim 1,wherein the thickener associates with the surfactant to more efficientlythicken the fluid.
 7. A fluid according to claim 1, wherein thethickener is a cross-linked polymer of carboxylic acids andhydrophonic-character cross-linking monomers.
 8. A fluid according toclaim 8, wherein the thickener is polyacrylic acid based polymer presentin the range of 50 ppm to 0.4 percent by weight.
 9. A fluid according toclaim 1, wherein the surfactant is nonionic and contains one or moreethoxylated alcohols containing a hydrophobic backbone of at least 6carbons and a hydrophilic group of at least 2 ethoxylates.
 10. A fluidaccording to claim 9, wherein the surfactant has a branched hydrophobicbackbone.
 11. A fluid according to claim 10, wherein the surfactant ispresent in the range of 50 ppm to 0.4 percent by weight.
 12. A fluidaccording to claim 1, wherein the surfactant does not include analkylphenol ethoxylate.
 13. A fluid according to claim 1, wherein the pHof the fluid is between 6.5-8.5 and the pH modifier is selected from thegroup consisting of sodium hydroxide, potassium hydroxide, analkylamine, and mixtures thereof.
 14. A fluid according to claim 13,wherein the pH of the fluid is between 6.9 and 7.5 and the pH controlmodifier is potassium hydroxide.
 15. A fluid according to claim 1,further comprising an anti-precipitant.
 16. A fluid according to claim15, wherein the concentration of the anti-precipitant is in the range of50 ppm to 0.2% by weight.
 17. A fluid according to claim 16, wherein theanti-precipitant is selected from the group consisting of polymericdispersants, aminocarboxylates, other biodegradable non-EDTA cheatingagents, and mixtures thereof.
 18. A fluid according to claim 1, furthercomprising 50 ppm to 0.2% by weight of a corrosion inhibitor.
 19. Afluid according to claim 18, wherein the corrosion inhibitor is selectedfrom the group consisting of carboxylates, phosphonates, sulfonates,amines, silicates, amides, and mixtures thereof.
 20. A fluid accordingto claim 18, wherein the corrosion inhibitor does not include compoundscontaining triazoles.
 21. A fluid according to claim 1, furthercomprising an anti-foaming agent, present in the range of 50 ppm to 0.2%by weight.
 22. A non-toxic fluid comprising: at least about 20% byweight of a freeze point depressant selected from the group consistingof short chain polyols having 3 to 5 carbon atoms, and mixtures thereof;at least about 10% by weight of water; a thickener; and a surfactant;the freeze point depressant providing a synergistic thickening effectcombined with the thickener and surfactant.
 23. A fluid according toclaim 22, wherein the freeze point depressant comprises glycerol.
 24. Afluid according to claim 22, wherein the thickener comprises a polymericthickener.
 25. A non-toxic fluid comprising: at least about 20% byweight of a freeze point depressant selected from the group consistingof short chain polyols having 3 to 5 carbon atoms, and mixtures thereof;at least about 10% by weight of water; a polymeric thickener; and asurfactant; a surfactant that functions as both a wetting agent andthickener.
 26. A non-toxic fluid comprising: at least about 20% byweight of a freeze point depressant selected from the group consistingof short chain polyols having 3 to 5 carbon atoms, and mixtures thereof;at least about 10% by weight of water; a thickener; and a surfactant;the fluid having a viscosity at 0.06 sec-1 shear rate and at 0° C. to−10° C. of at least 10,000 cP.
 27. A fluid according to claim 27,wherein the viscosity is at least 20,000 cP.
 28. A non-toxic fluidcomprising: at least about 20% by weight of a freeze point depressantselected from the group consisting of short chain polyols having 3 to 5carbon atoms, and mixtures thereof; at least about 10% by weight ofwater; a thickener; a surfactant; and an anti-precipitant that serves asecond function of helping to control the viscosity of the fluid.
 29. Afluid according to claim 28, wherein the anti-precipitant helps toreduce the viscosity.